Cathode ray tube control circuitry utilizing two accelerating windings



p 5, 1967 R. H. COMPTON ETAL 3,34

CATHQDE RAY TUBE CONTROL CIRCUITRY UTILIZING TWO ACCELERATING' WINDINGSFiled July 14. 1964 INVENTORS ROBERT H. COMP 7' ON BY OMER F. HAMAN/VROGER G. STEADMA/V wim ATTORNEY United States Patent ABSTRACT OF THEDISCLOSURE A cathode ray tube having an inner helical acceleratingelectrode and an outer helical electrode connected in parallel therewithto a source of high voltage for establishing equal voltage gradients onthe inside and outside of said tube. This arrangement of two parallelaccelerating electrodes produces faster stabilization of theaccelerating potential gradient when a new cathode ray tube is insertedinto the system.

The present invention relates to cathode ray tube control circuitry and,more particularly, to cathode ray tube control circuitry for reducingthe time required for establishing linearity in the voltage gradient ofthe electrostatic accelerating field set up within the tube.

A helical resistive accelerating electrode is often applied to theinside surface of a cathode ray tube for producing an electrostaticfield substantially parallel with the longitudinal axis of the tube,which field accelerates and directs an electron stream within the tube.In order to have uniform acceleration of the electron stream along thelongitudinal axis of the tube, the electrostatic voltage gradient shouldbe linear; that is, the rate of change of the field voltage with respectto distance along the length of the tube should be constant. However,when a tube is first installed into a system, it sometimes takes as longas several hours for the potential gradient between helix turns tostabilize and become linear due to random charge effects upon theoutside surface of the tube.

The portions of the glass envelope in between the turns of theaforementioned helical resistive electrode has a very low electricalconductivity, and, accordingly, considerable time may be required forthese portions of a newly installled tube to manifest the voltagegradient which tends to be set up due to the voltages applied to theinside tube surface by the helical electrode. In other words, randomcharge effects on the outside tube surface tend to create electrostaticvoltages which must be nullified by the voltages set up by the helicalelectrode. However, this process may take considerable time owing to theextremely low electrical conductivity of the glass envelope. During thisstabilization period, the electron beam is moved about in an undesirableand sometimes unpredictable manner by the changing charge pattern on theexternal surface of the tube.

Accordingly, it is the principal object of the present invention toprovide a new and improved device for making it possible to replace acathode ray tube in a precision display data readout system and attainthe desired accuracy within a few minutes thereby to sharply reduce themean repair time of such systems.

Other objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to thesole figure which discloses a preferred embodiment of the presentinvention.

The figure discloses a cathode ray tube 1 having a display screen 2situated at one end of the tube and having an electron gun 3 situated atthe other end of the tube. Helical accelerating electrode 4 is appliedto the inside wall of the tube and is connected to terminals 6 and 7,which in turn are connected to power supply 8 and switch 9, as shown. Aspower supply 8 may produce a voltage in the order of a few thousandvolts and as the helical electrode 4 is composed of resistive material,a linear electrostatic voltage gradient is eventually set up within thetube which is capable of accelerating the electron beam produced byelectron gun 3 and for directing it down the longitudinal axis of thetube. As explained hereinabove, when a cathode ray tube is firstinstalled, random charge effects occur on the outside wall of the tubewhich prevent the establishment of the linear electrostatic voltagegradient.

In the preferred embodiment of the present invention, helical resistiveelectrode 11 is evaporated or otherwise mounted on the outside surfaceof the tube in nonoverlapping relationship with accelerating electrode4, as shown, and is connected to terminals 6 and 7. As a result, anelectrostatic voltage gradient is set up on the outside surface of thetube which is substantially identical with the voltage gradient whichtends to be set up by helical electrode 4 on the inside of the tube.Accordingly, the aforesaid random charge effects are quickly nullifiedand the stabilization period is cut down from several hours to merely afew minutes.

It should be understood that helical is used herein in in the broadsense, that is, for describing a three-dimensional curve with one ormore turns about an axis. The turns need not have a constant slope andthe diameters of the turns may vary in an irregular manner.

While there has been shown and described a specific embodiment of theinvention, other modifications will readily occur to those skilled inthe art. It is not, therefore, desired that this invention be limited tothe specific arrangement shown and described, and it is intended in theappended claims to cover all modifications within the spirit and scopeof the invention.

What is claimed is:

1. In a cathode ray tube having a longitudinal axis, a helical resistiveaccelerating electrode mounted within said tube for providing anelectrostatic field generally oriented along the length of said tube, aDC voltage source having a first and second terminal, means for couplingsaid first terminal to one end of said helical resistive acceleratingelectrode, means for coupling said second terminal to the other end ofsaid helical resistive accelerating electrode so that a potentialgradient is set up inside of said tube substantially parallel with thelongitudinal axis of said tube, a resistive stabilizing electrodeadjacent with the outside surface of said tube for establishing avoltage gradient on the outside surface of said tube substantially equalto the voltage gradient set up on the inside of said tube by saidhelical resistive accelerating electrode, and means for applyingsubstantially the same potential across said stabilizing electrode as isapplied across said accelcrating electrode by said DC voltage source.

2. In a cathode ray tube having a longitudinal axis, a helical resistiveaccelerating electrode mounted within said tube for providing anelectrostatic field generally oriented along the length of said tube, aDC voltage source having a first and second terminal, means for couplingsaid first terminal to one end of said helical resistive acceleratingelectrode, means for coupling said second terminal to the other end ofsaid helical resistive accelerating electrode so that a potentialgradient is set up inside of said tube substantially parallel with thelongitudinal axis of said tube, a helical resistive stabilizingelectrode adjacent with the outside surface of said tube forestablishing a voltage gradient on the outside surface of said tubesubstantially equal to the voltage gradient set up on the inside of saidtube by said helical resistive accelerating electrode, and means forapplying substantially the same potential across said stabilizingelectrode as is applied across said accelerating electrode by said DCvoltage source.

3. In a cathode ray tube having a longitudinal axis, a helical resistiveaccelerating electrode mounted within said tube for providing anelectrostatic field generally oriented along the length of said tube, aDC voltage source having a first and second terminal, means for couplingsaid first terminal to one end of said helical resistive acceleratingelectrode, means for coupling said second terminal to the other end ofsaid helical resistive accelerating electrode so that a potentialgradient is set up inside of said tube substantially parallel with thelongitudinal axis of said tube, a helical resistive stabilizingelectrode adjacent with the outside surface of said tube forestablishing a voltage gradient on the outside surface of said tubesubstantially equal to the voltage gradient set up on the inside of saidtube by said helical resistive accelerating electrode, said helicalresistive stabilizing electrode being in non-overlapping relationshipwith the helical accelerating electrode, and means for applyingsubstantially the same potential across said stabilizing electrode as isapplied across said accelerating electrode by said DC voltage source.

4. In a cathode ray tube having an envelope and means for generating andprojecting an electron beam along an axis of said envelope, a resistiveaccelerating electrode wound on the inside of said envelope along atleast a portion thereof with at least one turn about said axis, and aresistive stabilizing electrode wound on the outside of said envelopewith at least one turn about said axis coordinate with said acceleratingelectrode over the same portion of said envelope, said acceleratingelectrode and said stabilizing electrode being connected in parallel forestablishing respectively identical voltage gradients at the inside andoutside of said envelope.

5. The combination defined in claim 4, wherein said resistivestabilizing electrode is in non-overlapping relationship with saidresistive accelerating electrode.

6. In a cathode ray tube having means for generating and projecting anelectron beam along an axis thereof, a resistive accelerating electrodewound with at least one turn about said axis within said tube, and aresistive stabilizing electrode wound with at least one turn about saidaxis outside said tube coordinate with said accelerating electrode andradially disposed with respect thereto, said accelerating electrode andsaid stabilizing electrode being connected in parallel for establishingrespectively identical voltage gradients inside and outside of saidtube.

References Cited UNITED STATES PATENTS 3,143,681 8/1964 Schlesingler3l531 X T. A. GALLAGHER, R. K. ECKERT,

I Assistant Examiners.

1. IN A CATHODE RAY TUBE HAVING A LONGITUDINAL AXIS, A HELICAL RESISTIVEACCELERATING ELECTRODE MOUNTED WITHIN SAID TUBE FOR PROVIDING ANELECTROSTATIC FIELD GENERALLY ORIENTED ALONG THE LENGTH OF SAID TUBE, ADC VOLTAGE SOURCE HAVING A FIRST AND SECOND TERMINAL, MEANS FOR COUPLINGSAID FIRST TERMINAL TO ONE END OF SAID HELICAL RESISTIVE ACCELERATINGELECTRODE, MEANS FOR COUPLING SAID SECOND TERMINAL TO THE OTHER END OFSAID HELICAL RESISTIVE ACCELERATING ELECTRODE SO THAT A POTENTIALGRADIENT IS SET UP INSIDE OF SAID TUBE SUBSTANTIALLY PARALLEL WITH THELONGITUDINAL AXIS OF SAID TUBE, A RESISTIVE STABILIZING ELECTRODEADJACENT WITH THE OUTSIDE SURFACE OF SAID TUBE FOR ESTABLISHING AVOLTAGE GRADIENT ON THE OUTSIDE SURFACE OF SAID TUBE SUBSTANTIALLY EQUALTO THE VOLTAGE GRADIENT SET UP ON THE INSIDE OF SAID TUBE BY SAIDHELICAL RESISTIVE ACCELERATING ELECTRODE, AND MEANS FOR APPLYINGSUBSTANTIALLY THE SAME POTENTIAL ACROSS SAID STABILIZING ELECTRODE AS ISAPPLIED ACROSS SAID ACCELERATING ELECTRODE BY SAID DC VOLTAGE SOURCE.